The present invention relates to bone screws, and particularly to interference screws for use in securing a tissue graft within a bone tunnel. More particularly, the present invention relates to a resorbable bone screw which may be used as an interference screw or as a soft tissue anchor screw.
Interference screws are screws which "interfere with" or drive a bone piece against a bone section or soft tissue graft. For example, in ACL surgery interference screws are often used to secure a bone block of a replacement graft within a bone tunnel. Such screws are often used as a wedge between the bone block and a pre-drilled tunnel wall in the tibia or femur in order to force the bone block against an opposite side of the tunnel wall so that bone ingrowth will fuse the bone block in place. In an ACL replacement, a tendon is typically harvested and then pushed or pulled through the tibial tunnel upwardly into the femoral tunnel. An interference screw is placed in the femoral tunnel to hold the upper bone block against the side of that tunnel.
Interference screws may be made from biocompatible metals, such as titanium or stainless steel. Interference screws may also be made from a wide variety of materials which are known to be resorbable into the body or which will promote bone growth in the tunnel to replace the screw. Preferred materials include PLLA or PLA (Poly-L-Lactide Acid) or cortical allograft bone. Other bioabsorbable materials which are eventually absorbed in the body are known and may be used to make interference screws as well. U.S. Pat. No. 5,364,400 to Rego, Jr. et al. showing an INTERFERENCE IMPLANT and U.S. Pat. No. 5,470,334 to Ross et al. showing a BIOABSORBABLE INTERFERENCE BONE FIXATION SCREW are examples of such screws and each are incorporated herein by reference.
In accordance with the present invention, a screw for use with soft tissue grafts is provided which includes a screw body having a tip portion formed to include a front face, an end portion formed to include a rear face, and a threaded portion extending between the tip portion and the end portion. The screw body further includes drive faces formed to define a passageway which extends from the front face of the tip portion to the rear face of the end portion. The drive faces of the passageway are further formed to extend from the front face of the tip portion to the rear face of the end portion. Preferably, the passageway has a polygonal cross-section. In a preferred embodiment, the polygonal cross-section is square.
In preferred embodiments, the polygonal shape of the passageway extends all the way through the screw body along an axial length of the screw body. The threaded portion of the screw body is formed to include a single thread forming thread segments having rounded crests and troughs in order to secure the soft tissue graft to bone, for example, without damaging the soft tissue graft. Preferably, the screw body is formed from a bioabsorbable material.
In further preferred embodiments, a driver is also provided to operate in combination with the screw body. The driver includes a screw-receiving portion and a handle portion positioned to lie in spaced-apart relation to the screw-receiving portion. In a preferred embodiment, the screw-receiving portion includes a body for being received within the passageway of the screw body and a tapered portion for extending beyond the front face of the tip portion of the screw body. The body of the screw-receiving portion is formed to be received through the passageway of the screw body so that drive faces of the body engage drive faces of the screw body and torsional and axial drive forces exerted by the driver are distributed along the entire length L of the screw body through the drive faces of the driver to the drive faces of the screw body. Optionally, the driver is cannulated for use with a guide wire.
Another aspect of this invention is a method of fixing a tissue graft within a bone tunnel. First, a bone tunnel is prepared to accept the graft. Next, the tissue graft is inserted within the tunnel. A screw having an axial passageway with a plurality of driving surfaces extending the entire length of the screw is driven into the bone tunnel by applying force along the entire length of each of the driving surfaces.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.